A new homologous series of nine [l-(p-n-alkylbiphenyl)3-(phenyl)propane]1,3-diones have been prepared and their mesomorphic properties studied. The first four homologues in the series exhibit the classical nematic phase and a smectic phase, the next five showing only a smectic phase. The optical textures, miscibility and the X-ray data establish that the smectic phase is of the A1 type. This is perhaps the first instance of a b.beta-diketone exhibiting a nematic as well as a smectic A1 phase. In addition, a few similar isomeric b.beta-diketones have also been synthesized to study the terminal substituent effect on the mesomorphic properties.